Field of the Invention
The present disclosure generally relates to information processing and more particularly, to a technique capable of three-dimensionally measuring a target object.
Description of the Related Art
Various types of methods are conventionally proposed to three-dimensionally measure a target object (e.g., a component of an industrial product). One of the conventional methods is a highly accurate and stable measuring method that includes projecting a predetermined projection pattern (e.g., a stripe pattern or a lattice pattern) on a measuring target object and capturing an image of the measuring target object. The method further includes obtaining a relationship between each image position (i.e., a pixel) of the captured image and a corresponding stripe position of the projection pattern, calculating the height of the measuring target object based on triangulation, and measuring a three-dimensional shape of the measuring target object.
In the above-mentioned three-dimensional measuring method, multiple reflections may occur if the measuring target object (e.g., a metallic member) is glossy. More specifically, a light pattern projected on one surface of a measuring target object may reflect on another surface of the measuring target object (may cause reflections a plurality of times) depending on the shape of the measuring target object. The reflection of light is referred to as primary reflection if it first reflects on a surface of the measuring target object. The reflection of light is referred to as secondary reflection if it sequentially reflects on two surfaces of the measuring target object. Further, the reflection of light is referred to as tertiary reflection if it sequentially reflects three times on the measuring target object. The above-mentioned secondary and higher-order reflections can be collectively referred to as multiple reflections. The multiple reflections can be also referred to as interreflection because reflections repetitively occur on different surfaces of a measuring target object. If multiple reflections occur, a glare appears although it is not originally present on the measuring target object. If the three-dimensional measuring processing is performed based on such a captured image, the measurement accuracy may deteriorate due to a noise caused by the glare.
To eliminate the glare, as discussed in Japanese Patent Application Laid-Open No. 2008-309551, it is conventionally proposed to dim or quench a part of the projection pattern that causes multiple reflections on surfaces of an inspected object. More specifically, it is conventionally known to project two types of different light patterns and obtain a three-dimensional shape based on each of these light patterns. Then, if there is a significant difference between two three-dimensional measurement results in a target area, it can be determined that multiple reflections are generated in this area. Further, the conventional method includes performing ray tracing to detect a surface on which multiple reflections occur, quenching a projection pattern portion that corresponds to the detected surface, and correcting the three-dimensional measurement result based on a captured image obtainable by projecting a newly quenched pattern on a measuring target object.
The method discussed in Japanese Patent Application Laid-Open No. 2008-309551 is disadvantageous in that the processing is complicated and takes a relatively long time because the ray tracing is performed to detect a projection pattern portion that causes multiple reflections.